Current military threat detection optical sensors are optimized to work against “traditional” threats such as heat-seeking surface-to-air missiles targeting aircraft. In many cases, these systems do not provide desired and required capabilities to address new threats. These new threats include unsophisticated weapons, such as those used by irregular militia in Afghanistan, as well as advanced weaponry developed by modern adversaries.
Both the unsophisticated and the advanced weapons pose similar challenges to detector technology. The first issue is sensor speed. For unsophisticated weapons, fast sensing is required to detect brief events such as gunfire muzzle flash. For advanced weaponry, some new missiles employ high-speed maneuvering designed to defeat older systems that operate at slower rates. To successfully address the full range of threats, modern sensors need to operate at rates greater than 1000 frames per second. A rate of 4000 frames per second will allow a sensor system to address the full range of potential threats and to provide capabilities such as threat identification that are highly desired.
A second issue is precision threat location. Systems require highly precise identification of threat locations so that countermeasures can be employed. Examples of precision threat location are locating a sniper and tracking a missile. Providing advanced automated countermeasures and counterattacks requires higher precision than is currently available in many sensors. Examples would be automatic return of weapons fire, or laser designation of enemy hostile fire.
Unfortunately, increasing the precision of threat location is a competing requirement with high-speed operation. Higher optical precision is typically accomplished through higher resolution imagery, which means more pixels in each frame. Increasing both the total frame rate and the total number of pixels in each frame (pixel count) can result in an unacceptably large increase in total input/output (I/O) signals or data. For example, some very capable sensors today operate at 1000 frames per second with a 256×256 sensor. To achieve 4000 frames per second with a 1K×1K sensor (1 megapixel) would require 64× higher I/O. This large data rate would require the replacement of most system components, rather than an upgrade of the sensor only. Furthermore, some technology components to handle this large data rate might not be available, or would be prohibitive in cost, size, weight, or power.
Accordingly, it is an object of the present invention to increase resolution without increasing pixel count to achieve high-precision, high-speed detection (sensing) capabilities that can be used against newer threats.
It is another object of the present invention to provide said sensing capabilities in a manner that is relatively inexpensive, compact, lightweight, and powerful.
It is still another object of the present invention to provide said sensing capabilities in a manner that can be incorporated as an upgrade to existing systems.
The invention described herein increases resolution without increasing pixel count. In fact, pixel counts can be reduced by a factor of four or more so that total I/O does not increase as the frame rate is increased. This allows high-precision, high-speed sensing in a configuration that fits within the system “footprint” of legacy sensors. Using this approach, it is possible to upgrade existing systems by replacing sensor modules only: total system replacement is not required. The invention therefore enables higher retrofitting of existing systems to attain precision and increased detection capability against newer threats.
The following patents may be relevant to the field of the invention:
U.S. Pat. No. 7,333,181 to Scott et al., incorporated herein by reference, discloses a sensor chip assembly that contains a focal plane array constructed as a semiconductor chip with two interconnected layers. The first layer comprises multiple position sensing detectors made from infrared sensitive semiconductor material and arranged in an array of position sensing detectors. The second layer is made of trans impedance amplifiers and associated on-chip signal processing elements made from an electronic semiconductor material.
U.S. Pat. No. 6,815,790 to Bui et al., incorporated herein by reference, discloses a position sensing detector for improved resolution and accuracy in two-dimensional positions sensing in the 1.3 to 1.55 micron wavelength region.
U.S. Pat. No. 6,462,326 to Cleaver, incorporated herein by reference, discloses an electronic circuit that adapts the output of a position sensing detector, designed to determine the position of an incident CW laser beam, to determine the position of a fast pulsing laser incident on the detector's surface.
U.S. Pat. No. 5,723,869 to Costa et al., incorporated herein by reference, discloses a position sensing detector with a plurality of electronically isolated sensing channels containing ends and an output current lead at each end of each channel.
U.S. Pat. No. 6,528,788 to Galloway, incorporated herein by reference, discloses a method for determining the position of an object within an area viewed by a single detector of an array, in which signals from detectors adjacent to the single detector are compared with each other and/or the single detector. The method can be extended to larger objects to ascertain the location of edges.
U.S. Pat. No. 6,373,050 to Pain et al., incorporated herein by reference, discloses a circuit for reading a signal from an infrared detector, which includes a current-mode background-signal subtracting circuit having a current memory which can be enabled to sample and store a dark level signal from the infrared detector during a calibration phase.
U.S. Pat. No. 6,147,340 to Levy, incorporated herein by reference, discloses a background suppression technique using well-controlled and repeatable charge skimming operations to increase the charge capacities of the integration capacitors of integrated focal plane readout unit cells.
U.S. Pat. No. 5,128,543 to Reed et al., incorporated herein by reference, discloses a time-of-flight analyzer, such as a secondary ion surface analyzer, and methods are disclosed wherein a beam of charged particles is created, magnified, directed along a path to a detector, detected and the time of flight measured.
It is also known in astronomy to de-focus an image of a star (a subpixel light source) on a pixel array to create a blur detected by multiple pixels, and to interpolate the position of the star as the center of the blur.